Securely identifying a device using a DNS-controlled proxy

Systems and methods for identifying a device identifier of a computing device using a browser. A proxy executing on a computing device holds open a connection request from a browser and establishes a secure connection between the proxy and a web server. The proxy sends the first user identifier and the device identifier to a web server. The web server stores the first user identifier and the device identifier as an entry in a cache. The proxy then connects with the browser and establishes a secure connection between the browser and the web server via the proxy. The proxy receives and forwards a second user identifier from the browser to the web server. The web server determines that the second user identifier matches the first user identifier, extracts the associated device identifier, and sends the device identifier to the browser via the proxy.